It must have been typical for Ethan’s dad to leave his weapons not locked up. Ethan ws able to post photos of the new gun and even fire it for a practice run.
Ethan is the killer here and needs to be locked away, but his dad is also complicit by leaving his weapons and ammo unsecured.
This is a similar situation to the Sandy Hook killer, except the SH kid was mentally unstable like VERY MUCH SO. His mommy thought it would be wonderful to give him full access to high powered firearms. Welp, he killed her first. This dad should feel fortunate to be alive IMO.